1. Field of Invention
This invention relates generally to cementitious building materials. More specifically, it relates to a light-weight cementitious building material composition and method of making such a material.
2. State of the Prior Art
Concrete is, of course, a well-known cementitious building material that has had great utility in construction for many years. Concrete is generally considered to be a composition comprised of Portland cement, sand, aggregate, and water. Often an air entraining agent is used to trap small bubbles of air in the mixture to minimize the deleterious effects of freeze/thaw cycles. In addition, a bonding agent can be used to increase the structural strength of the material, as well as to enhance bonding of the material to the aggregate, reinforcing steel, and the like. Portland cement is a generic term for a hydraulic-setting cement material, the principle active constituent of which is powdered or pulverized calcium silicate.
The powdered calcium silicate reacts with water to harden into a solid mass of cementitious material. The sand, i.e., silicon dioxide (SiO.sub.2), and aggregate provide the bulk fill material of the concrete that is solidly bound together by the hardened Portland cement (calcium silicate) to form the hard, solid concrete building material.
One of the problems with concrete, at least for many applications, is that it is very heavy. Thus, much of the structural strength designed into concrete structures must be to support the concrete load itself. Also, concrete is not a very effective insulator, thus concrete building structures require extra insulation for effective heat and energy control.
There have been developments of more light-weight concrete. One approach to reducing the weight of concrete is to use lighter weight filler material or aggregate. U.S. Pat. No. 4,214,911, issued to J. Siejko, et al, is an example of this kind of light weight concrete, wherein the sand fraction of the waste material of combustion of brown coal is dry ground (i.e., pulverized cinder blocks) and used as a substitute for sand. The pulverized cinder blocks are mixed with cement and hot (50.degree. C.) water, and a pore-producing material (i.e., foaming agent) is added.
The U.S. Pat. No. 3,625,723, issued to R. Sicka discloses another method of producing a light-weight insulating ceramic material. Sicka's process also utilized calcium silicate (i.e., Portland cement) as the hydraulically setting cement bonding material with fly ash derived from combustion of pulverized coal as an inexpensive filler material. Sicka also discloses the use of wallsonite, magnesium silicate, and zircon as suitable fillers.
Other well-known light weight concrete materials are made by substituting light weight aggregate, such as volcanic ash or vermiculite in place of the heavier rock aggregates used in conventional concrete. Such light weight concretes, however, have less compressive strengths than conventional concrete.
As noted in the above-referenced Sicka and Siejko, et al, patents the abundance of inexpensive fly ash has attracted attention for its potential uses in construction materials in recent years.
Fly ash is a relatively common waste product of coal fired installations, and as such is available in certain locations at very low cost. This availability and low cost has resulted in numerous proposals to use fly ash as a building material.
Some of the proposed uses have been as a component in concrete, either by adding the fly ash to the concrete mix, or by first treating it in some manner. The treatment processes include classifying, heating, crushing, pelletizing, and forming the fly ash into an aggregate such as in the Sicka and Siejko et al patents referenced above. The U.S. Pat. No. 3,852,084 issued to W. Webster and the Japanese Pat. No. 1970-51512 (Public Patent Request Notice 50-13297) to Nippon Peroxide Co. are additional examples of such uses in which fly ash is used with pulverized lime or cement. Some other proposed uses for fly ash include binding it together into shapes, panels, or other articles by using various adhesives, or using it in fire resistant coatings. Most of these materials use a bonding process that depends on either pretreatment of the fly ash, or use of an adhesive that drives up the cost of the finished product, destroying much of the cost advantage of the raw material.
U.S. Pat. No. 3,700,470 issued to P. Barton is of interest in that it achieved the production of a foamed ceramic material utilizing fly ash without Portland cement, calcium silicate, or crushed lime. However, Barton's process requires heat, along with an amphoretic metal, such as aluminum, lead, tin, or chromium, which is capable of reacting as an acid or as a base, in order to achieve the desired curing and other properties.
U.S. Pat. No. 3,700,470 discloses a foamed composition for use in insulating wallboards, comprising fly ash or other materials in combination with powdered metal, water, and sodium silicate, which is molded and heat cured in order to form a final product. R. C. Valore, Jr. in an article in the ACI Journal of November, 1956, discussed foamed concrete produced by controlled mixing of mixtures containing gas forming chemicals such as hydrogen peroxide and calcium hypochlorite (ref page 512).
The above-referenced Japanese Pat. No. 1970-51512 (Public Patent Request Notice 50-13297) issued to Nippon Peroxide Co. dislcoses the use of hydrogen peroxide as a foaming agent in a foamed concrete material that includes fly ash as an ingredient. However, it also includes cement and requires heat for curing and hypochlorite as a foaming retarder.
While there are a number of attempts in the prior art to utilize fly ash in the production of an inexpensive, light weight, insulating cementitious building material, none of those approaches have been able to achieve that result without the use of heat or the addition of Portland cement or a functional equivalent, such as calcium silicate or crushed lime, and other more expensive additives, such as amphoretic metals, aluminum hydroxide, magnesium or barium, carbonate, etc.
The within invention is an improvement over prior art in that it uses a combination of foaming agent, air entrainer, and a minimum of low cost bonding agent in order to produce a material with good utility and no requirement for heat curing or critical mixing procedures. The invention thereby provides increased utility for on-site fabrication and reduces manufacturing costs for pre-formed articles.
Accordngly, it is a general object of the present invention to provide a method of making an inexpensive light weight, insulating cementitious building material.
It is another object of the present invention to provide a practical utilitarian use for fly ash as an inexpensive building material.
It is a more specific object of this invention to provide a method of producing a light weight, insulating cemetitious building material utilizing fly ash as the principle hydraulically setting cementitious material, but without the necessity of using heat, hot water, or expensive preparations and additives that complicate the process and drive up the cost.
Additional objects, advantages and novel features of the invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by the practice of the invention. The object and the advantages of the invention may be realized and attained by means of the instrumentalities and in combinations particularly pointed out in the appended claims.
The present invention provides a novel process and product in that the mix comprises fly ash, water, bonding agent, air entrainer, and a chemical foaming agent consisting of either an oxygen-producing agent such as hydrogen peroxide; or a carbon dioxide producing reaction such as sodium carbonate, sodium bicarbonate, or calcium carbonate and an acid such as acetic acid in a water solution. The components are mixed and allowed to foam and harden into a low density masonry like material which has insulating properties and is resistant to freezing, fire, thermal shock, and moisture. It is suitable for such applications as structural elements of buildings, either precast or formed in place; for thermal insulation; or for use as a lightweight aggregate. The material can also be applied as an insulating coating on existing structures.
Additives or optional components may be used with the basic recipe to accelerate or retard the setting time, to increase the early strength or final strength or both, to improve water resistance, or to vary the appearance of the final product. Fabrication procedures and additives suitable for ordinary concrete generally are suitable for use with the composition disclosed herein.